Monitoring structural transformations in crystals. 11. Yang photocyclizations – one type of reaction, but diversity of structural changes

Abstract

Structural changes proceeding in a crystal during the Yang photocyclization of the salt 6,6-diethyl-5-oxo-5,6,7,8-tetrahydronaphthalene-2-carboxylate with (1S)-1-(4-methylphenyl)ethylamine were monitored by means of X-ray structure analysis. The course of the photoreaction was evaluated on the basis of the geometrical parameters for the pure reactant crystal. Variations in the cell constants, the product content, the geometry of the reaction centre, the orientation of molecular fragments and the geometry of hydrogen bonds were described and analyzed. It was found that the cell volume increased until 56% product content and decreased thereafter. The distance between the directly reacting C atoms was constant, approximately 3.0 A, until approximately 75% reaction progress. Analysis of the distance between atoms that would participate in the formation of the second (unobserved) enantiomorph excluded the formation of such an isomer. Molecular fragments varied their orientation during the photoreaction, and the largest change was observed for the carboxylate group despite its participation in strong hydrogen bonds. The geometry of the hydrogen bonds changed during the photoreaction. The largest change was 0.17 A for the D...A distance and 13 degrees for the D-H...A angle. A comparison of the intra- and intermolecular parameters for the studied salt with data for other compounds undergoing the Yang photocyclization in crystals revealed a diversity of structural changes brought about by this type of photochemical reaction.

Monitoring structural transformations in crystals. 12. Course of an intramolecular [4 + 4] photocycloaddition in a crystal

“…The type of variation in the cell volume for the photoreaction of (1) is similar to that for the intermolecular [4 + 4] photocycloaddition of 9-methylanthracene (Turowska-Tyrk & Trzop, 2003). However, in the case of the intermolecular [2 + 2] photocycloadditions (Nakanishi et al, 1980(Nakanishi et al, , 1981Turowska-Tyrk, 2003) and also the intramolecular formation of a cyclobutane ring in the Yang photocycloadditions (Turowska-Tyrk, Bą kowicz & Scheffer, 2007;Turowska-Tyrk, Łabę cka, Scheffer & Xia, 2007;Turowska-Tyrk, Trzop, Scheffer & Chen, 2006), no similarities between types of variations in the cell volume were observed. Moreover, the size of the change was also different for different compounds undergoing the same kind of photochemical reaction.…”

“…The aim of our studies carried out in recent years was the monitoring of structural changes in crystals by means of X-ray structure analysis. We concentrated on intermolecular [2 + 2] and [4 + 4] photocycloadditions (Turowska-Tyrk, 2001Turowska-Tyrk & Trzop, 2003) and the unimolecular formation of a cyclobutane ring, namely the Yang photocycloaddition (Turowska-Tyrk, Bą kowicz & Scheffer, 2007;Turowska-Tyrk, Łabę cka, Scheffer & Xia, 2007;Turowska-Tyrk, Trzop, Scheffer & Chen, 2006). It should be emphasized that [2 + 2] photocycloadditions were also monitored by others (Fernandes & Levendis, 2004;Ohba & Ito, 2003).…”

Monitoring Structural Transformations in Crystals. Part 15. Structural Changes in Crystals Caused by UV Radiation Despite the Lack of a Photochemical Reaction

“…In the case of intra-and intermolecular chemical processes, a cell volume can change by several percent [4,[7][8][9][10][11]. It is interesting that even for one type of a chemical reaction, cell constants and a cell volume for different compounds can change in a different manner [34,35].…”

“…Although, the changes are small, they are statistically significant at the 3r level. For chemical reactions the changes in orientation of molecular fragments are usually much bigger, namely even ca 20° [5][6][7][9][10][11].…”

“…In the recent decade the papers on monitoring photochemical reactions in crystals by means of X-ray structure analysis have started to appear in the scientific literature [1][2][3][4][5][6][7][8][9][10][11][12]. Those papers have provided the knowledge on structural changes brought about by photochemical reactions, in particular in a reaction center and positions of molecules in crystals.…”